It happened in the community of Maywood, where a 16-year-old Proviso East High School student is seen being attacked from behind by another girl. The attacker slams the girl's head into the wall and grabs her by her hair.
What really bothers the local sheriff is the reaction of everyone watching.
"Then to have people jumping up and down, celebrating and then to have people pulling out cell phones, someone videotaping this and putting it on YouTube, it's horribly upsetting," said Cook County Sheriff Tom Dart.
"There's nothing pleasant about this," Dart said. "It's very disturbing."
Two teenage girls have since been charged with aggravated battery and mob action. A third was charged with mob action for recording it.
Here's the story and video.